1. Field of the Invention
The present invention relates to a monolithic ink-jet printhead and a method of manufacturing the same, and more particularly, to a monolithic ink-jet printhead including a nozzle plate having a good hydrophobic property and an effective adhering property, and a method of manufacturing the same.
2. Description of the Related Art
In general, ink-jet printheads may eject ink droplets using an electro-thermal transducer (ink-jet type), which generates bubbles in ink by means of a heat source.
FIG. 1 is a schematic perspective view illustrating the structure of a conventional ink-jet printhead, and FIG. 2 is a schematic cross-sectional view of the ink-jet printhead shown in FIG. 1. Referring to FIGS. 1 and 2, an ink-jet printhead includes a manifold (not shown) to which ink is supplied, a substrate 1 on which a heater 12 and a passivation layer 11 protecting the heater 12 are formed, a passage plate 2 which forms an ink passage 22 and an ink chamber 21 on the substrate 1, and a nozzle plate 3 which is formed on the passage plate 2 and has an orifice 31 corresponding to the ink chamber 21.
In general, a passage plate and a nozzle plate are formed by a photolithography process using polyimide. In a conventional ink-jet printhead, the passage plate and the nozzle plate are formed of the same material, for example, polyimide. The nozzle plate may be easily detached from the passage plate due to a weak adhering property of polyimide.
In order to solve this problem, in a conventional method to manufacture an ink-jet printhead, when a passage plate and a nozzle plate are formed of polyimide as separate layers as described above, the passage plate and the nozzle plate are separately formed and are bonded with a substrate. In this method, due to several problems, including structural misalignment, the nozzle plate cannot be attached to a substrate such as a wafer, and the nozzle plate should be attached to each chip separated from the wafer. Thus, this method results in low productivity.
Meanwhile, in conventional methods of manufacturing an ink-jet printhead, a mold layer is used as a sacrificial layer to form an ink chamber and an ink passage.
In the conventional methods, a sacrificial layer is formed of a photoresist on a substrate to correspond to patterns of an ink chamber and an ink passage, polyimide is coated to a predetermined thickness on the sacrificial layer, and a passage plate and a nozzle plate are formed as a single body. Then, an orifice (nozzle) is formed in the nozzle plate, and the sacrificial layer is finally removed such that the ink chamber and the ink passage are formed below the nozzle plate. In the conventional methods of forming an ink passage and a nozzle using a mold layer, the passage plate and the nozzle plate are formed of polyimide to protect the mold layer. However, the plates and the mold layer cannot be hard-baked at a sufficient temperature, since the mold layer is formed of a photoresist having a low heat-resistant property. Due to the presence of the mold layer, the passage plate or nozzle plate formed of polyimide cannot be hard-baked. In addition, the non-hard-baked passage plate or nozzle plate is damaged by an etchant when the mold layer used to form the ink passage and the ink chamber is removed. In particular, a portion where the passage plate contacts the nozzle plate is etched, and an interface between the passage plate and the nozzle plate damaged by the etchant becomes unstable, and thus becomes loose.
The nozzle plate of an ink-jet printhead is directly opposite to the recording paper and has several factors that affect the ejection of ink droplets ejected through a nozzle. Among these factors, when a hydrophobic property on the surface of the nozzle plate is low, that is, when the surface of the nozzle plate has a hydrophilic property, part of the ink ejected through the nozzle flows out of the surface of the nozzle plate, contaminates the surface of the nozzle plate, and the size, direction, and speed of the ejected ink droplets become nonuniform. As described above, the nozzle plate formed of polyimide has a hydrophilic property, and thus has the above-mentioned problems. In order to solve the problems caused by a hydrophilic property, in general, a coating layer for a hydrophobic property should be additionally formed on the surface of the nozzle plate formed of polyimide. Metals, such as plated nickel (Ni), gold (Au), palladium (Pd), or tantalum (Ta), and a perfluoronated alkane and silane compound having a high hydrophobic property, such as fluoronated carbon (FC), F-Silane, or diamond like carbon (DLC), are used as the coating layer. The hydrophobic coating layer may be formed by wet etching, namely, spray coating or spin coating, and may be deposited by dry etching, namely, plasma enhanced chemical vapor deposition (PECVD) and sputtering. Using the coating layer that has a hydrophobic property causes an increase in costs for an ink-jet printhead.